1. Field of the Invention
The present invention relates to a self-dispersible metal complex colorant comprising an azo moiety, and more particularly, to a self-dispersible metal complex colorant which may be uniformly dispersed in a solution without a separate dispersing agent, have high stability during long-term storage, embody various colors and have effective fastness, such as light resistance, water resistance and the like.
2. Description of the Related Art
In general, colorants are substances which exhibit inherent colors by selectively absorbing and reflecting visible light. Colorants are used in various fields embodying colors, such as fibers, foods, drugs, cosmetics, coatings, ink for inkjet printers or printing, pigmenting plastics or rubbers, manufacturing furniture, textile printing, and making papers or ceramics.
Colorants are classified into dyes and pigments. Dyes are colorful substances that may be dissolved in water or oil and dispersed as single molecules, and may bind to molecules such as fibers for dyeing. Pigments are substances that do not dissolve in water or oil and form an opaque colorful film in the form of a powder on a surface of a material.
In general, dyes may have a wide range of colors that are bright and vivid. However, dyes are not light/water resistant, i.e., they may be bleached/discolored by light or may be diluted by water or organic solvents. On the other hand, pigments have more effective light/water resistance than dyes. However, pigments have a narrower range of colors than dyes. Thus, much research has been conducted to enhance light and water resistance, and the like of dyes, without reducing the variety of colors of dyes. One such dye includes a metal complex.
U.S. Pat. No. 5,095,100 discloses a method of producing a metal complex dye having an improved light resistance by forming coordinate bonds between the metal and an azo group and a specific functional group in the dye molecule. However, the method requires the presence of the azo group and the specific functional group in the dye molecule, thus limiting the types of the colorants to which the method may be applied. In addition, a metal complex dye obtained by forming coordinate bonds with the metal tends to have less solubility than dyes without coordinate bonds.
In general, dispersing agents are used to prevent formation of precipitates in a solution or aggregation of pigment particles. Dispersing agents prevent interactions between the pigment particles due to electrostatic or steric hindrance, thus allowing the insoluble pigment particles to be stable in the solution. However, conventional dispersing agents have a large molecular weight. Even a small change in an amount of dispersing agent used may cause a large change in rheology, such as viscosity, of an ink composition. Thus, it is very important to control the amount of the dispersing agent used in the production of the ink composition.
Thus, there is a need to enhance light resistance and water resistance while maintaining the inherent color of the dye by forming a metal complex in a colorant, such as a dye or a pigment, and to prevent the reduction of solubility of the dye and insolubility of the pigment due to the introduction of the metal complex by using a self-dispersible ligand.